The problem of filtering a liquid containing contaminant particles in industrial applications without excessive manual operations or overly complex mechanical structure has long persisted. A reliable low-maintenance fine filter is needed to remove solids from wastewater samples, thereby insuring accurate analysis of the remaining liquid.
Various filtering methods have previously been employed. For example, a replaceable cartridge filter such as U.S. Pat. No. 3,495,463 provides a filter cartridge on a support means within a funnel shaped cavity. Though the filter cartridge is easily removable, filters such as these tend to absorb organic material and bleed it back into the sample stream over a long period of time. This can mask concentration peaks and make accurate analysis of a liquid sample a considerable problem. Furthermore, since said filters do encounter significant bleeding problems, they must be changed frequently.
Russian Pat. No. 251,242 discloses a tape filter device having a pivoting arm which is operated by a pneumatic system. The pivoting motion of the arm connects the sample liquid to the filter device. The filter device is situated such that the filter tape is vertically drawn across its surface. This device hampers the production of a uniform sample of filtered liquid since there is a build-up of solid matter at the bottom portion thereof. The vertical movement of the filter tape as the sample liquid is flowing through it, coupled with this build-up of solid material, prevents this device from providing a fresh filtering surface.
U.S. Pat. No. 3,471,017 discloses that a filter band or ribbon may be passed through inlet and outlet ports in a filtering apparatus across the path of material flow and that an adequate seal may be maintained at the inlet and outlet ports by carefully maintaining a solidified plug of the material within the ports as a sealant. A difference in size between the inlet plug and the outlet plug is relied upon to advance the filter band through the apparatus. To insure a complete seal of the plugs utilized in this apparatus, they must be sufficiently cooled to form a relatively solid mass which tends to bind in the inlet and outlet ports, and this makes filter screen changing difficult. If the plugs are formed in a less solid state, undesirable leakage of material occurs. Additionally, some materials do not exhibit an ability to form an adequate solidified plug. Furthermore, this apparatus utilizes high pressures associated with an extrusion process that force the filter band to dimple into the access holes of the back-up or breaker plate supporting the filter band. This makes it extremely difficult to change the position of the filter band. This patent is a relatively complicated device, which affords limited filter area, requires frequent changes of the filter media, and has a complicated mechanism to avoid leakage of contaminated liquid around the edges of the filter medium.
Another type of filter device, the "Fox Filter" Research Disclosure, 13356, (May 1975), has a tapered filter head which is "grooved and shaped" such that a strip of filter tape may be guided across a channel drilled through the side of the filter head. Filtered liquid is induced to flow through the tape into a channel located within the filter head via gravity or a vacuum. The filter head is mounted within a weir box having an inlet channel and an outlet channel. Liquid sample is fed into the weir box and allowed to overflow through the outlet channel located in the upper portion of the reservoir. The tapered configuration of the filter head provides poor sealing around the tape to filter head interface thereby allowing solid waste materials to contaminate the filtered sample. The apparatus is designed such that the weir must be drained before the filter can be changed and it must be disassembled for cleaning. Furthermore, the flow pattern through the rectangular weir box causes said weir to fill with solids above the tape head. The filter tape may thereby become clogged with solid material.
A need therefore, exists for a reliable low-maintenance fine filter to remove solids from wastewater samples.
The present invention provides a simplified apparatus which avoids leakage of contaminated liquid around the edges of the filter media through the unique configuration of the tape head, and provides a fresh filtering surface to avoid buildup of solid material on the filter media.
The present invention provides a liquid filter medium with a maximum of surface area which enables the filter medium to accommodate a sample of larger volume.
The unique design of the weir of the present invention prevents the buildup of solid material in the liquid channeling device.
The present invention provides an apparatus for intermittent or continuous sampling of liquid media.